Hearing loss is generally caused by sensorineural hearing loss, conductive hearing loss or a combination of the two. Sensorineural hearing loss, occurs when there is damage to the inner ear (i.e., the cochlea) or to the nerve pathways from the inner ear to the brain. Sensorineural hearing loss is not generally correctable using medicines or surgery and is unfortunately the most common type of permanent hearing loss. Conductive hearing loss occurs when sound is not conducted efficiently through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear. Conductive hearing loss usually causes a reduction in sound level or the ability to hear faint sounds. Unlike sensorineural, conductive hearing loss can often be corrected medically and/or surgically.
Sensorineural hearing loss is the most common type of hearing loss among adults (occurring in 80 percent of adult hearing loss cases). Although sensorineural hearing loss is not often medically or surgically treatable, the use of hearing aids often helps. However, contemporary hearing aids do not work very well at helping the wearer hear sounds when the wearer himself is speaking, since the speaker's own sounds tend to get over amplified. The over amplification is due in part to natural phenomenon that occurs when the ear canal is blocked (particularly by a hearing aid). People with normal hearing can simulate this phenomenon by placing a finger in an ear and listening to their own speech. To address this issue, one approach is to providing venting holes in the part of a hearing aid that gets inserted in the ear canal. Another approach lowers the output gain of the hearing aid in lower frequencies, which correspond to the added sound heard by the wearer when he or she is speaking. However, these approaches often reduce the effectiveness of the hearing aid when the user is not talking.